github.com/ledgerwatch/erigon-lib@v1.0.0/common/hexutility/text.go (about)

     1  /*
     2     Copyright 2021 Erigon contributors
     3  
     4     Licensed under the Apache License, Version 2.0 (the "License");
     5     you may not use this file except in compliance with the License.
     6     You may obtain a copy of the License at
     7  
     8         http://www.apache.org/licenses/LICENSE-2.0
     9  
    10     Unless required by applicable law or agreed to in writing, software
    11     distributed under the License is distributed on an "AS IS" BASIS,
    12     WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
    13     See the License for the specific language governing permissions and
    14     limitations under the License.
    15  */
    16  
    17  package hexutility
    18  
    19  import (
    20  	"encoding/hex"
    21  	"fmt"
    22  )
    23  
    24  const (
    25  	badNibble = ^uint64(0)
    26  )
    27  
    28  // UnmarshalFixedText decodes the input as a string with 0x prefix. The length of out
    29  // determines the required input length. This function is commonly used to implement the
    30  // UnmarshalText method for fixed-size types.
    31  func UnmarshalFixedText(typeName string, input, out []byte) error {
    32  	raw, err := checkText(input, true)
    33  	if err != nil {
    34  		return err
    35  	}
    36  	if len(raw)/2 != len(out) {
    37  		return fmt.Errorf("hex string has length %d, want %d for %s", len(raw), len(out)*2, typeName)
    38  	}
    39  	// Pre-verify syntax before modifying out.
    40  	for _, b := range raw {
    41  		if decodeNibble(b) == badNibble {
    42  			return ErrSyntax
    43  		}
    44  	}
    45  	_, err = hex.Decode(out, raw)
    46  	return err
    47  }
    48  
    49  func checkText(input []byte, wantPrefix bool) ([]byte, error) {
    50  	if len(input) == 0 {
    51  		return nil, nil // empty strings are allowed
    52  	}
    53  	if bytesHave0xPrefix(input) {
    54  		input = input[2:]
    55  	} else if wantPrefix {
    56  		return nil, ErrMissingPrefix
    57  	}
    58  	if len(input)%2 != 0 {
    59  		return nil, ErrOddLength
    60  	}
    61  	return input, nil
    62  }
    63  
    64  func bytesHave0xPrefix(input []byte) bool {
    65  	return len(input) >= 2 && input[0] == '0' && (input[1] == 'x' || input[1] == 'X')
    66  }
    67  
    68  func decodeNibble(in byte) uint64 {
    69  	switch {
    70  	case in >= '0' && in <= '9':
    71  		return uint64(in - '0')
    72  	case in >= 'A' && in <= 'F':
    73  		return uint64(in - 'A' + 10)
    74  	case in >= 'a' && in <= 'f':
    75  		return uint64(in - 'a' + 10)
    76  	default:
    77  		return badNibble
    78  	}
    79  }